Emissions standards for vehicles with internal combustion engines continue to become more stringent. For both on and off highway vehicles with diesel engines, a common exhaust after treatment to reduce NOx emissions is the use of a Selective Catalytic Converter (SCR) in the exhaust pipe. The desired chemical reactions in the SCR are enhanced by the injection of a urea solution into the exhaust pipe, upstream of the SCR device.
Typically, a particulate trap or similar filter device is also situated in the exhaust pipe. Such devices must be periodically regenerated, and a common approach is to inject a hydrocarbon liquid into the exhaust stream, which combusts and thereby produces sufficient heat to regenerate the device.
It is desirable that a similar injector be provided for use with both the SCR device and the filter device.
There are currently two known types of SCR urea systems being utilized.
One system includes an air pump, a urea solution storage tank, a low pressure metering pump controlled by an electronic control unit, a nozzle that feeds into the air line, and a catalyst located in the engine exhaust. The air line feeds the mix of air and urea solution into the exhaust upstream of the catalyst. Quantity control is determined via operating frequency of the metering pump.
A newer, airless system includes a urea solution storage tank, a motor driven pump that pressurizes the urea solution through a line, and into a magnetically actuated injector controlled by an electronic control unit. The injector feeds an atomized urea solution plume into the exhaust upstream of a catalyst. Quantity control is determined via operating frequency and duration of the injector.
It is well known in the industry that all SCR urea systems add significant cost and complexity to any vehicle platform.